EUV (“extreme ultraviolet”) lithography systems are used in the semiconductor manufacturing industry to produce feature sizes of smaller dimensions and patterns with superior resolution compared to other lithography systems. EUV lithography systems utilize light with very small wavelengths in the vicinity of about 13.5 nanometers which lies in the spectrum between visible light and x-ray. The shortened wavelength enables higher resolution and the accurate production of smaller features. EUV optics in EUV lithography systems utilize mirrors and other reflective surfaces to direct the EUV light beam to the reticle and substrate being patterned. Reflective surfaces are used instead of lenses because all matter absorbs EUV radiation. Quartz lenses would absorb a lot of EUV photons.
The EUV photolithography system produces a pattern on a photoresist coated substrate. The pattern is generally produced by directing beams of EUV light to a partially reflective, partially absorbent reticle that includes a device pattern. The EUV light beams are reflected from the reticle and impinge upon the substrate surface where the light radiation chemically alters the exposed photoresist. Because air also absorbs EUV photons, EUV lithography operations often take place in a chamber maintained at or near vacuum conditions, i.e. at low pressure.